From the first operation to repair a heart in 1891 until the early 1950""s, heart surgeons were limited by the problem of trying to work on the heart while it was still beating. The heart""s constant motion, and the presence of blood that obscured the surgeon""s view, made repairing heart defects a surgical challenge. Surgeons had to work quickly and there was always a danger of disrupting blood circulation to vital organs. The solution to this problem came in the late 1950""s with the development of the first oxygenator.
The veins return deoxygenated blood to the heart""s right atrium. From the right atrium, blood is pumped to the right ventricle, then through the pulmonary artery to the lungs. The lung oxygenates the blood while removing carbon dioxide as it passes through the lung""s alveolar capillary network. Oxygenated blood is then returned to the left atrium by way of the pulmonary veins. Blood is then pumped through the mitral valve into the left ventricle and pumped back into the body""s circulatory system. Cells are replenished with oxygen and carbon dioxide is taken up by the blood as the blood passes through the body""s capillary system. After this gaseous exchange is accomplished, the blood is returned to the heart and the cycle is repeated.
During cardiopulmonary by-pass (CPB) surgery, for example, venous blood is taken from the patient""s circulation by means of a cannula placed in the vena cava. The blood xe2x80x9cby-passesxe2x80x9d the heart and lungs and enters what is referred to as the xe2x80x9cextracorporeal circuitxe2x80x9d or literally a circuit xe2x80x9coutside the body.xe2x80x9d Oxygenation of the patient""s blood takes place in an oxygenator much in the same way as it does in the natural process. After the blood is oxygenated and temperature regulated, it is returned to the patient""s arterial circulation through a cannula so that the patient""s body may utilize the oxygenated blood.
Early blood oxygenators were called xe2x80x9cbubblersxe2x80x9d because they bubbled air up through a column of blood, diffusing oxygen into the blood and carbon dioxide out. The problem was that this bubbling action created foam which not only was damaging to the blood, but also rendered this portion useless to the patient.
A defoaming sponge was employed to break down the bubbles of foam back into usable liquid blood. However, the raw sponge by itself was ineffective without a surface agent to lower the surface tension of the blood foam. Silicone Antifoam xe2x80x9cAxe2x80x9d by Dow Corning was adopted throughout the industry as the defoaming agent of choice. It is comprised of silicone oil and approximately 4.5% silica particles (approximately 5 micrometer (i.e., micron) in diameter). Another development was the use of blood reservoirs to process blood suctioned (scavenged) from the patient during surgery. Antifoam A was used to coat defoaming sponges used in blood reservoirs here as well.
The silicones used in typical silicone antifoams are hydrophobic. Therefore, these compounds are typically dissolved in organic solvents in order to prepare an antifoam solution, which can be applied to a surface to reduce foaming of liquids contacting the surface. The primary solvents that have been used heretofore are chlorofluorocarbons (CFCs) because they are nonflammable and evaporate quickly. Unfortunately, because of recent concerns that CFCs affect the earth""s protective ozone layer, the production and use of CFCs will cease in the near future. Thus, there is a need in the art for alternative defoaming compositions having fewer if any detrimental side effects to the individual and the environment.
The present invention provides compositions comprising (and preferably, consisting essentially of) lecithin, such as soy lecithin, and preferably inorganic particles, such as silica particles, and optionally a diluting agent. Such compositions are particularly suitable as defoaming (i.e., antifoaming) compositions. Typically, such compositions are coated on a surface of an article, such as a surface in a cardiotomy reservoir. Alternatively, however, compositions of the present invention can be added directly to a liquid prone to foaming.
Preferably, compositions of the present invention also include a diluting agent, such as water or alcohol. Optionally, compositions of the present invention can include a silicone. In preferred compositions, the ratio of diluting agent to lecithin is at least about 7:1 parts diluting agent to lecithin, and the amount of inorganic particles is preferably about 2 weight-% to about 20 weight-% inorganic particles, based on the weight of the lecithin in the composition.
Surfaces on which compositions of the present invention can be coated for desired effect include surfaces of devices through which liquids prone to foaming pass or are stored, for example. This includes portions of extracorporeal circuits, particularly cardiotomy reservoirs. Alternatively, instead of being directly coated on a surface of a device through which a liquid passes or is stored, compositions of the present invention can be coated on articles that are placed in such devices, such as defoaming sponges, which are often open cell sponges, for example.
The present invention also provides a method of reducing foaming in a liquid prone to foaming. The method includes contacting the liquid prone to foaming with an antifoam composition comprising lecithin and inorganic particles, wherein the amount of foam present in the liquid combined with the antifoam composition is decreased relative to the same liquid under the same conditions without the antifoam composition. Such liquids prone to foaming include, for example, blood, milk, beer, and soda.
The composition can be added to the liquid prone to foaming or be coated on a surface with which the liquid comes in contact. Such methods are typically performed during surgery, such as cardiopulmonary surgery, orthopaedic surgery, and thoracic surgery, and are used to reduce foaming in blood. Preferably, at least one characteristic of foaming in a liquid, such as blood, is reduced. That at least one characteristic is selected from the group of wicking, streaming, spotting, scud formation, and backup/overflow.
Significantly, by reducing foaming in blood, trauma to the blood can be reduced. Thus, the present invention provides a method of reducing trauma to blood in an extracorporeal circuit comprising combining blood with a composition comprising lecithin and inorganic particles. This combining step typically occurs by coating one or more surfaces of the extracorporeal circuit or an article therein, such as a sponge, with which the blood comes in contact with the antifoam composition.
Definitions
A xe2x80x9ccardiotomy reservoirxe2x80x9d can be part of a device used to store blood that has been removed from a patient until the blood is returned to the patient. The xe2x80x9ccardiotomy reservoirxe2x80x9d includes a surface, e.g., a defoaming sponge, that is used to decrease the amount of foam in the blood removed from the patient, and the reservoir into which blood flows immediately following treatment to decrease foaming. The device that of which the xe2x80x9ccardiotomy reservoirxe2x80x9d forms a part is referred to as an xe2x80x9cextracorporeal circuit.xe2x80x9d Extracorporeal circuits include, for example, oxygenators, reservoirs, filters, tubing, connectors, valves, sensors, and devices used to scavenge blood from a patient during surgery.
xe2x80x9cFoamxe2x80x9d refers to a gas dispersed in a liquid such that bubbles are formed. xe2x80x9cDefoam,xe2x80x9d xe2x80x9cdefoamed,xe2x80x9d and xe2x80x9cdefoamingxe2x80x9d refer to decreasing the amount of foam in a liquid by decreasing the amount of gas dispersed in the liquid. The amount of foam present in a liquid can be determined by, for instance, measuring the volume of foam present on top of the liquid containing the foam.
xe2x80x9cDefoaming spongexe2x80x9d refers to a surface that can be used to decrease foaming of a liquid. Typically, a liquid prone to foaming flows through the defoaming sponge and causes a decrease in the amount of foam in the liquid. A xe2x80x9cdefoaming spongexe2x80x9d is typically an open cell sponge.
A xe2x80x9cliquid prone to foamingxe2x80x9d refers to a liquid that, when subjected to certain conditions including, for instance, oxygenation or mixing, forms a foam.